Black absorbs the heat in the summer. Very hard to find one to purchase (limited amount are made each year).

I got this for Christmas this year, great bag, I can fit a 1d with a 70-200 and a 10d with a 17-40 or shorter inside the bag along the middle strip. Then there's room for plenty of other lenses / flashes / filters etc. It fits very snuggly on my back and is comfortable to have on, the padding also makes me think my camera gear is safe, haven't fallen yet with it though.

I also like that it's not a camera brand bag so it doesn't draw attention in shifty parts of town, also the rear entry is nice for accessing the camera gear, as well as preventing theft.